1. Field of the Invention
The present invention relates to a method for manufacturing a solar cell module. More particularly, the invention relates to a method for manufacturing a solar cell module in which undulation of the laminate, defects in external appearance, and the like caused by deformation or breakage of a photovoltaic cell, rupture of covering materials, and unevenness in a foamed member can be prevented.
2. Description of the Related Art
A solar cell module, obtained by covering a photovoltaic cell with a resin and bonding a foamed member on the back surface of the cell, has been known as a solar cell module which can be carried outdoors and which can be used for outdoor activities and the like. Such a solar cell module having a bonded foamed member can even float on water.
Conventionally, solar cell modules which can be used for outdoor activities and the like have been manufactured according to a method in which a foamed member is bonded after laminating members to an insulator. In this method however, two processes, i.e., a process of laminating the members with insulator and a process of bonding the foamed member, are required. In order to manufacture a solar cell module with lower cost, simplification of these processes is required.
A solar cell module, in which a back-surface lid member having a space with an amorphous-silicon-type solar cell panel is mounted on a surface opposite to a photosensing surface of the solar cell panel, and a foaming synthetic resin is filled in the space formed between the solar cell panel and the back-surface lid member, has been proposed (Japanese Patent Laid-Open Application (Kokai) No. 8-116082 (1996)). It is claimed that, according to such a configuration, a temperature for recovering or suppressing photodegradation in an amorphous-silicon-type solar cell can be maintained.
There are various methods for covering an amorphous-silicon thin-film photovoltaic cell. For example, a method of using a plastic film, instead of a glass plate, as a surface covering material, and a method of using a steel plate or the like as a back-surface covering material, when intending to provide rigidity, have been known. A method of using a single-vacuum-type chamber in a process for covering a photovoltaic cell with such a member has been proposed. In this method, an O-ring is provided on a laminator plate, and evacuation is performed using a rubber plate or the like. A description will now be provided of a process of covering a photovoltaic cell with a surface covering material and a back-surface covering material using a single-vacuum-type chamber.
There are two methods, i.e., a face-up method and a face-down method, in a process for covering a photovoltaic cell with a surface covering material and a back-surface covering material.
In the face-up method, a back-surface covering material, a photovoltaic cell and a surface covering material are laminated in this sequence on a laminator plate having an O-ring. After mounting silicone rubber or the like on this structure, the inside surrounded by the laminator plate, the O-ring and the silicone rubber are vacuum-heated. Then, the entire structure is placed in an oven heated to a predetermined temperature and is heated for a predetermined time period. The face-down method differs from the face-up method only in that the sequence of lamination of the covering materials and the photovoltaic cell are inverse to the sequence in the face-up method.
One of these two methods can be selected in consideration of various conditions, such as the shape of the photovoltaic cell, the thicknesses of the covering materials, projections and recesses on components to be mounted, and selection of a surface for which smoothness is required. For example, when projections on the surface of the photovoltaic cell are large and the surface covering material is thin, the face-up method is selected. On the other hand, when the surface covering material is sufficiently thick and projections on the surface of the photovoltaic cell are large, the face-down method may also be adopted. In the face-down method, since the metal plate of a jig presses the surface of the solar cell module, the surface of the solor cell module is smoothed. On the other hand, in the face-up method, since the surface of the solar cell module is pressed by the silicone rubber or the like, the surface of the solar cell module follows the shape of the surface of the photovoltaic cell.
Problems when foaming an unfoamed member in the covering process
It has become clear that the following problems arise when using the above-described single-vacuum-type laminating device in a process in which an unfoamed member is included in the back-surface covering material. In the process, the photovoltaic cell is covered with the surface covering material and the back-surface covering material, and a foamed member is formed at the back surface side of the photovoltaic cell.
That is, in the face-down method, since a lid member, comprising silicone rubber or the like, used as a jig has a low flexural rigidity (i.e., is flexible), a central portion of the silicone rubber tends to be stretched due to pressure during foaming if an unfoamed member is foamed while fixing the end portions of the silicone rubber. As a result, the foamed member present at a central portion of the solar cell module contains a greater amount of foam, thereby causing inhomegeneity.
On the other hand, in the face-up method, since the foamed member can be pressed with the photovoltaic cell, a homogeneous foamed member can be obtained in a portion below the photovoltaic cell. However, the expansion of the generated foams differs between a portion where the photovoltaic cell is present and a portion where the photovoltaic cell is absent. Hence, it is necessary to solve this problem.
Problem of deformation of the photovoltaic cell in the covering process
Currently, the covering material of the solar cell is being made thinner in order to reduce the cost of the solar cell module. For this reason, the covering process according to the above-described face-up method is preferably used.
However, when covering the photovoltaic cell having projections on the back surface according to this method, the photovoltaic cell, during the covering process, is pressed following the projections on the back surface, resulting in deformation or even destruction of the photovoltaic cell.
Problem of nonuniform foaming
In the unfoamed member, a foaming agent contained therein is subjected to thermal decomposition to form a foamed member after the resin is heated and melts.
When covering the photovoltaic cell according to the face-up method, the unfoamed member flows while being heated and melted, so that the amount of the resin in portions corresponding to the projections of the back surface of the photovoltaic cell decreases. Even if the foaming agent decomposes in this state, a foamed member is not formed in these portions because the amount of the resin is very small. Accordingly, the formed foamed member becomes nonuniform. This nonuniform foaming causes depressions in the back surface of the solar cell module.
In the face-up method, by providing a lamination base during the covering process which has a shape conforming to the back surface of the photovoltaic cell, it is possible to prevent the flow of the resin and the deformation of the photovoltaic cell. However, since the obtained solar cell module is partially protruded, this approach is not preferable from the viewpoint of external appearance. Furthermore, when moving the solar cell module outdoors, the protruded portions tend to be selectively abraded, thereby causing breakage of the covering material.
Although the problem of the flow of the resin can be solved by causing the silicone rubber to follow the unfoamed member by adopting the face-down method, the above-described nonuniform foaming between central portions and end portions occurs. If pressure is provided by inserting a member having a high flexural rigidity between the silicone rubber and the unfoamed member, defects occur in the external appearance due to the resin flow.
Problem of undulation of lamination materials
When the expansion of generated foams differs and the thickness of the solar cell module partially changes, the surface of the solar cell module is undulated, resulting in the formation of defects in external appearance. Particularly, in the case of lamination materials using an unfoamed member, since the expansion of generated foams greatly differs between portions where the photovoltaic cell is present and portions where the photovoltaic cell is absent, undulation of the surface covering material and/or the back-surface covering material tends to occur.